文章第2段倒数第2句， 第3句信息与问题句信息一致， 因此问题句提供了正确信息。
考点：代词结构指代内容 + 定语从句
4. The key(关键，钥匙， 键) components(成分， 部件) of a computer mouse are the two LEDs(二极管).
A. right B. wrong C. not mentioned
4.A. 利用问题句中的饱含数字的特征结构two LEDs 作为答案线索， 在文章中查找答案相关句：
The basic computer mouse is an amazingly clever invention with a relatively simple design that allows us to point at things on the computer and it is very productive. Think of all the things you can do with a mouse like selecting text for copying and pasting, drawing, and even scrolling on the page with the newer mice with the wheel. Most of us use the computer mouse daily without stopping to think how it works until it gets dirty and we have to learn how to clean it. We learn to point at thing before we learn to speak, so the mouse is a very natural pointing device. Other computer pointing devices include light pens, graphics tablets and touch screen, but the mouse still our workhorse.
The computer mouse was invented in 1964 by Douglas Englehart of Stanford University. As computer screens became popular and arrow keys were used to more around a body of text, it became clear that a pointing device that allowed easier motion through the text and even selection of text would be very useful. The introduction of the mouse, with the Apple Lisa computer in 1983, really started the computer public on the road to relying on the mouse for routine computer tasks.
How does the mouse work(工作)? We have to start at the bottom, so think upside down for now. It all starts with mouse ball. As the mouse ball in the bottom of the mouse rolls over the mouse pad, it presses against and turns two shafts. The shafts are connected to wheels with several small holes in them. The wheels(轮子， 滚轮) have a pair of (一对，一双 )small electronic(电子) light-emitting(发光的) devices(设备) called light emitting diodes (LED) mounted on either side(被安装在两侧的).(第7句) One LED (发光二极管)sends a light beam(光束) to the LED on the other side(在对面). As the wheels(轮子/滚轮) spin(旋转) and a hole(孔，洞) rotates by, the light beam(光束) gets through to (与...电话联系， 达到)the LED on the other side(在对面). But a moment(瞬间) later(后来) the light beam is blocked (被阻塞)until the next(下一个的， 下一次) hole is in place(在适当的位置). The LED(发光二极管) detects(察觉， 探测) a changing(变换的) pattern(模式， 图案) of light(光), converts the pattern into(把...转变成) an electronic(电子的) signal(信号), and sends(发送， 寄，派遣) the signal to the computer(计算机) through(通过) wires(电线) in a cable (电缆)that goes out the mouse body. This cable is the tail that helps give the mouse its name. The computer interprets the signal to tell it where to position the cursor on the computer screen.
以上答案相关句涉及到两个发光二极管在鼠标中的具体工作方式：二极管把光信号转换成电信号， 传送到电脑。 由此可看出二极管是鼠标中的关键部件。
考点：概括总结
5. When an ordinary(普通的) computer mouse(鼠标) gets dirty(脏的), it has to be replaced (不得不被替换)with a new one.
A. right B. wrong C. not mentioned
5.B. 细节题。利用问题句中的含有修饰词的细节信息结构new one(new mouse)及另一个修饰词dirty 共同作为答案线索作为答案线索， 在文章中查找答案相关句：
The basic computer mouse is an amazingly clever invention with a relatively simple design that allows us to point at things on the computer and it is very productive. Think of all the things you can do with a mouse like selecting text for copying and pasting, drawing, and even scrolling on the page with the newer mice with the wheel. Most of us use the computer mouse daily without stopping to think how it works until it gets dirty and we have to learn how to clean it. We learn to point at thing before we learn to speak, so the mouse is a very natural pointing device. Other computer pointing devices include light pens, graphics tablets and touch screen, but the mouse still our workhorse.
The computer mouse was invented in 1964 by Douglas Englehart of Stanford University. As computer screens became popular and arrow keys were used to more around a body of text, it became clear that a pointing device that allowed easier motion through the text and even selection of text would be very useful. The introduction of the mouse, with the Apple Lisa computer in 1983, really started the computer public on the road to relying on the mouse for routine computer tasks.
How does the mouse work? We have to start at the bottom, so think upside down for now. It all starts with mouse ball. As the mouse ball in the bottom of the mouse rolls over the mouse pad, it presses against and turns two shafts. The shafts are connected to wheels with several small holes in them. The wheels have a pair of small electronic light-emitting devices called light emitting diodes (LED) mounted on either side. One LED sends a light beam to the LED on the other side. As the wheels spin and a hole rotates by, the light beam gets through to the LED on the other side. But a moment later the light beam is blocked until the next hole is in place. The LED detects a changing pattern of light, converts the pattern into an electronic signal, and sends the signal to the computer through wires in a cable that goes out the mouse body. This cable is the tail that helps give the mouse its name. The computer interprets the signal to tell it where to position the cursor on the computer screen.
So far we have only discussed the basic computer mouse that most of you probably have or have used. One problem with this design(设计) is that the mouse gets dirty as the ball rolls over(在...上面滚过) the surface (表面)and picks up(捡起, 获得, 加快) the dirt(灰尘). Eventually(最终) you have to clean(把...弄干净) your mouse. The newer optical mice avoid this problem by having no moving parts.
责任编辑：虫虫
